Rescuers are working to find survivors amid the rubble of buildings destroyed in a massive explosion at a fertiliser plant in the US state of Texas.
Between five and 15 people are thought to have been killed by the explosion at the fertiliser company in the town of West, near Waco.
More than 160 people were injured and dozens of buildings destroyed, and some officials suggest the final death toll could be higher.
Three or four volunteer firefighters are among the missing after the explosion, which produced a tremor equivalent to a small earthquake, the BBC reports.
An official said on Thursday the situation remained volatile because of an extremely dangerous substance, ammonium nitrate, found at the scene.
Earlier, police said the plant was storing tanks of anhydrous ammonia, a less flammable fertiliser.
The site is being treated as a crime scene though police say there is no indication that the blast and a fire which preceded it were anything other than industrial accidents.
Texas state Governor Rick Perry said he was declaring the area a disaster and would request an emergency declaration for federal aid from US President Barack Obama, who had offered any help needed.
He said air quality and gas pipelines were being monitored for safety and gas supplies had been disconnected until any risk had passed.